Method:
Chop the onions and fresh tomatoes into small pieces and finely chop the garlic and keep aside.
Heat olive oil in a pan and add onion. and garlic together
When the onion has softened add tomatoes and cook till it becomes soft and then add basil leaves.
Cover the pan with the lid and leave to simmer on low heat for 15 to 20 min. Switch off heat.
Once its cool, grind to a smooth paste.
Add more hot water if required, then season it with salt and pepper.
Bring to boil and remove.

I like an oven roasted version: Heat oven to 425. Mix seeded fresh tomatoes, onions, whole peeled garlic, s&p, and olive oil in a roasting pan and roast until blackened in spots (30 mins or so). Add to a pot with some chicken broth; simmer for 20 mins. Add fresh basil. Blend with a hand blender or in a regular blender until smooth. Add some cream or whole milk. Enjoy!